1. When atoms combine to form molecules, their individual atomic orbitals lose their identity and form new orbitals called molecular orbitals.
2. The shape of molecular orbitals depend upon the shapes of combining atomic orbitals.
3. The number of molecular orbitals formed is the same as the number of combining atomic orbitals. half the number of molecular orbitals formed will have lower energy and are called bonding orbitals, while the remaining half molecular orbitals will have higher energy and are called anti-bonding molecular orbitals.
4. The bonding molecular orbitals are represented as σ (sigma), π (pi), δ (delta) and the corresponding anti-bonding orbitals are called σ* , π* and δ*.
5. The electrons in the molecule are accommodated in the newly formed molecular orbitals. The filling of electrons in these orbitals follow Aufbau’s Principle, Pauli’s exclusion principle and Hund’s rule as in the case of filling of electrons in the atomic orbitals.
6. Bond order gives the number of covalent bonds between the two combining atoms.
The bond order of a molecule can be calculated using the following equation:
= \(\frac{N_b-N_a}{2}\)
Nb = Number of electrons in bonding molecular orbitals.
Na = Number of electrons in anti-bonding molecular orbitals.
7. A bond order of zero value indicates that the molecule does not exist.
